Spectrum Measurements
R&S
®
ESR
426
User Manual 1175.7068.02 ─ 12
Risk of hearing damage
To protect your hearing, make sure that the volume setting is not too high before put-
ting on the headphones.
The volume for the headphones is controlled using the rotary knob next to the "AF Out-
put" interface on the front panel of the instrument.
For span > 0, the demodulation is not continuous. The frequency at which the demodu-
lation takes place is determined by the active marker. The demodulation bandwidth
corresponds to the RBW. If the level of the selected frequency is above the threshold
line, the sweep stops for the selected time (stop time) and the RF signal is demodula-
ted. For span = 0, the demodulation is continuously active irrespective of the stop time
set.
Frequency Measurement with the Frequency Counter
In order to accurately determine the frequency of a signal, the R&S
ESR is equipped
with a frequency counter which measures the frequency of the RF signal at the inter-
mediate frequency. Using the measured IF, the R&S
ESR calculates the frequency of
the RF input signal by applying the known frequency conversion factors.
The frequency measurement uncertainty depends only upon the accuracy of the fre-
quency reference used (external or internal reference). Although the R&S
ESR always
operates synchronously irrespective of the set span, the frequency counter delivers a
more exact result than a measurement performed with a marker. This is due to the fol-
lowing:
●
The marker measures only the position of the point on the trace and infers from
this value the signal frequency. The trace, however, contains only a limited number
of points. Depending upon the selected span, each point may contain many mea-
surement values, which therefore limits the frequency resolution.
●
The resolution with which the frequency can be measured with a marker is depend-
ant on the selected resolution bandwidth, which in return affects the necessary
measurement time. For this reason, the bandwidth is normally defined as wide as
possible and the sweep time as short as possible. This results in a loss of fre-
quency resolution. For the measurement with the frequency counter, the sweep is
stopped at the reference marker, the frequency is counted with the desired resolu-
tion and then the sweep is allowed to continue.
In I/Q Analyzer mode (see
on page 458), the resolution
with which the frequency can be measured with a marker is always the filter band-
width, which is derived from the defined sample rate.
Measurement of Noise Density
During noise measurement, the noise power density is measured at the position of the
marker. For span = 0, all points of the trace are used to determine the noise power
density. For span > 0, two points to the right and left of the marker are used for the
measurement to obtain a stable result.
Analysis
